Language is a main communication tool of human beings. More and more communications occur between different languages in globalization. In our daily life, it is common to read articles, reports or papers written in foreign languages. Though some people have learned foreign languages, it is still common for them, as non-native speakers, to encounter unfamiliar words or phrases, especially while reading technical articles in the foreign languages.
Electronic documents (e.g., electronic books and articles) can be displayed on personal computers and portable electronic devices. These electronic documents are prevailing and replacing paper documents. By using electronic documents, a user can easily switch between two tasks including reading and writing, or to perform both tasks at a same time. Electronic documents also have advantages in reading articles in foreign languages. For example, when a user is reading, translation applications may provide real-time translation assistance. These translation applications, however, may present problems, for example, when they are configured to automatically translate contents of electronic documents.